A conventional seat belt comprises a length of seat belt webbing connected at three points to load-bearing parts of a vehicle. The seat belt webbing is designed to have a lap portion that passes laterally across the hips of a seat occupant, and a torso portion that passes diagonally across the torso of the seat occupant from one hip to the opposite shoulder.
Typically one end of the seat belt webbing is attached to a sill anchor that is bolted to a load-bearing longitudinally extending structural member of a vehicle on one side of a seat, usually between the seat and an adjacent door. The lap and torso portions of the seat belt join at a buckle mechanism on the opposite side of the seat. The torso portion of the seat belt webbing is attached to a seat belt retractor mounted to a load-bearing part of the vehicle, for example a side pillar or sill, or directly to a structural member of a seat.
The seat belt retractor increases comfort for the seat occupant restrained by the belt since it allows the seat belt webbing to pay out under relatively low loads to enable limited movement of the restrained seat occupant, for example to reach in-car entertainment controls or storage compartments. However the seat belt retractor is biased to keep the seat belt webbing relatively taut about the seat occupant and a locking element locks the seat belt retractor against the payout of seat belt webbing in the event an acceleration sensor detects a rapid acceleration or deceleration indicative of a crash.
The seat belt webbing is fastened to the buckle mechanism by a buckle tongue that is attached to the seat belt webbing. The buckle tongue can slide on the seat belt webbing so that the proportions of the seat belt webbing making up the lap and torso portions can easily be varied to reflect the size of the seat occupant.
Known seat belt restraints of this sort tend to be unsuitable for vehicle occupants of shorter than average stature, particularly for children, because the upper fastening point of the torso portion of the seat belt is fixed to accommodate an average person and is fixed at or above the height of the back of the seat. This is particularly so in a seat belt installation for a rear seat.
Thus the torso portion of the seat belt webbing tends to be badly positioned for a child or short person and usually passes too close or adjacent to the neck of the child or short person. Because the child or short person does not fit into the adult seat belt properly a shoulder of the child or short person can roll out of the seat belt during a crash effectively making the seat belt a two-point lap belt only. In addition the child may slide under the lap portion; this is known as submarining. It is well known that children feel uncomfortable with adult seat belt restraints and often position the torso portion behind their back to reduce discomfort.